# Trigonomic Identities Help?

• December 18th 2008, 03:10 PM
ArthurYanthar
Trigonomic Identities Help?
I have trouble proving this. Thanks for any help in advanced!

Prove the following:

tanxsinx tanx - sinx
tanx + sinx = tanxsinx
• December 18th 2008, 03:42 PM
Krizalid
$\frac{\tan (x)\sin (x)}{\tan (x)+\sin (x)}=\frac{\tan (x)\sin (x)\left( \tan (x)-\sin (x) \right)}{\tan ^{2}(x)\sin ^{2}(x)}=\frac{\tan (x)-\sin (x)}{\tan (x)\sin (x)}.$

Observe that $\tan ^{2}(x)-\sin ^{2}(x)=\sin ^{2}(x)\left( \frac{1}{\cos ^{2}(x)}-1 \right)=\tan ^{2}(x)\sin ^{2}(x),$ and we're done. $\blacksquare$